Non-staining transfer sheet



March 1, 1960 c. DAVIS 2,

NON-STAINING TRANSFER SHEET Filed Aug. 13, 1957 IVJ/////////////////////////% I- f k\\\\\\ \MB A BASE WEB B =COAT|NG CONTAINING NONSTAINING TRIARYLMETHANE COMPOUND INVENTOR.

CHESTER DAVIS ATTORNEY NON-STAINING TRANSFER SHEET Chester Davis, Newport, Ky.

Application August 13, 1957, Serial No. 677,838

13 Claims. (Cl. 117-36) duplicating master sheet containing Crystal Violet Oleate,

for example, may give from two to five times more satisfactory copies than an azo dye-forming master sheet. Unfortunately, copy papers containing these triphenylmethane dyes cause permanent chemical staining of skin and clothing fabrics; and workers in the recording field have long sought methods of overcoming this basic defect.

The reduction of the triphenylmethane dye salts to their colorless leuco compounds and the conversion of these dye salts to the colorless carbinol bases by means of strong alkalis has been proposed in one form or another by previous workers in the recording field; but these substances are readily converted back to the intensely colored dyes by skin and clothing with strong chemical adsorption. Davis and Th-acker (US. 2,646,367) have utilized certain colorless triphenylmethane lactones which are nonstaining to skin; but these materials are extraordinarily unstable to light and moisture in the colored form. What is needed for a successful commercial nonstaining transfor sheet is a series of triphenylmethane dye compounds which are substantially nonstaining to skin and clothing, cheap to manufacture, reasonably light-stable in the colored form and giving on a suitable surface intensely colored characters which are resistant to decoloration by high humidity and adverse atmospheric conditions.

The author of the present invention has discovered that suitable introduction of'nitro groups into triphenylmethane dyes has the effect of lowering the dissociation constant of the resultant nitrated color base to a level where the dye is too weakly basic to give a stable chemical compound with skin tissue yet is still sufficiently basic to give intensely colored salts with suitable acids, including the paper coating clays and acid silicates which have long been used for paper coatings in the copy paper field.

The resultant nitrated color bases and their salts are covered in a co-pending application, namely my application Serial No. 677,837, filed August 13, 1957, for Nonstaining Color Bases and Their Use. These bases are yellow to orange-red in color, stable, and readily yield light-stable, intense prints on suitable receiving sheets. Transfer sheets containing Dinitro Crystal Violet Carbinol Base (I) and Dinitro Malachite Green Base (II), for example, may be safely handled without leaving intense violet or green stains on the skin; yet transfer sheets containing these materials will give intense characters upon a suitable receiving sheet.

Previous workers in the recording field have concen- U s s t a nt eration.

trated their investigations upon attempts to obtain completely colorless derivatives of the triphenylmethane dyes; these workers failed to realize that the most desirable property of transfer sheets is a complete lack of stain and not a complete lack of color, which is a secondary consid- A colored recording system of high intensity but lacking in chemical staining is far more desirable than a colorless recording system of low tinctorial power, low stability, or which stains the skin. It is, therefore, not the purpose of the present invention to claim an absolutely colorless transfer sheet; the point to be emphasized is the lack of permanent chemical stain possessed by nonstaining transfer sheets of the present invention.

If one examines the structure of Crystal Violet Carbinol Base (III), it is obviously a very strong base due to the high electron density around the central carbon atoms charged core; and the carbinol hydroxide ion can contribute to the screening of the central carbon atoms core only at very small proton concentrations; ,i.e., only at high hydroxyl ion concentrations (strongly basic solutions). If one forms the mononitro derivative of III, the resultant structure (IV) is stable at a higher proton concentration because here the quanticule of one benzene ring is less free to shield the central carbon core; and the, screening contribution of the hydroxide ion quanticule is more strongly needed. The mononitro derivatives is, however, still strongly staining. Upon dinitration, however, the resultant structure (I) is such that now two quanticules are less free to screen the central core; and the hydroxyl qu'anticule is now strongly required for screening the central carbon core. In brief, the dissociation constant is decreased; and Dinitro Crystal Violet Carbinol Base is a weak base. The Trinitro Crystal Violet Carbinol Base (V) has such a strong screening requirement forthe hydroxide ion quanticule that dissociation can occur only at high proton con centration, and V is a very weak base.

i NMe: III

NMer

N Me'a ot the nonsta'ining color bases would be preferable to the "use of the free bases; this permits the use of an ordinary "paper receiving'sheet-in place of a specially coated receiving sheet. The use of oleic acid and organic acids suchas trichloracetic acid, benzenesulfonic acid, tannic acid, etc. is "ideal for these applications. Any colored salts which accidentally contact fibers can then be easily removed by treatment with a mild alkali (soap, ammo- "niu'rn hydroxide solution triethanolamine, etc.) and subsequent washing with'wafer or a woolcleaning solvent such as carbon tetrachloride.

All that is essential *for the materials to be used in the nonst'aining transfer sheet of the present invention is a reduction of the dye base dissociation constant to a value sufficiently below pK 7 that reaction with skin tissue and textile fibers is negligible; this is brought about in the present invention by the suitable introduction of nitro groups into a triphenylmethane dyes aromatic ring. The best results are obtained by nitration until the dissociation constant of there'sultant dye base lies between 2 and 5. While the results obtained by dinitration of Crystal Violet and Malachite Green are of special interest be causefof the fundamental simplicity and low cost of these structures, a wide range of triphenylmethane dyes and theirclosed ring analogues may be used in the nonstaining transfer sheet of the present invention.

a For certain applications, where addition or" an external acid to form the colored dye salt is not desirable, transfer sheets containing inner salts (zwitterions of sulfonic acid groups may be obtained by using materials obtained by sulfonation of the desired color base with fuming sulfuric acid or by forming the dye with a sulfonated starting material. These inner salts are intensely colored salts and give intensely colored transfer sheets; but the transfer sheets thus produced need no specially coated receiving sheet.

Description A 3% solution of 2,2'-dinitro-4,4',4" tris (dimethylamino) triphenyl'carbinol in chlorinated diphenyl of 42% chlorine content (Arachlor 1242) is prepared; and this is emulsified in a 20% solution of polyvinyl alcohol "in water, 'using three parts by weight of chlorinated diphenyl solution to one part by weight solid polyvinyl alcohol. The resultant emulsion is coated onto a base paper and passed over a heated drum to remove water.

The bright yellow coating effectively differentiates the coatcd 'sidc from the uncoated side. When the coated 4 side is placed in contact with an activated silica-coated receiving sheet, pressure applied "to the "upper im'c'da'ea) side transfers the recording fluid to the clay-coated receiving sheet to give an intense violet (almost blue-black) print.

A 3% solution of 2,2-dinitro-4,4-bis (dimethylamino)-triphenylcarbinol inchlorinated diphenyl of 42% chlorine content (Arachlor 1242) is emulsified in a 20% aqueous polyvinyl alcohol solution, using three parts of chlorinated diphenyl solution to one part solid polyvinyl alcohol by weight. The resultant emulsion is coated onto a standard base paper stock and passed over a heated drum to remove water. The bright yellow coating effectively differentiates the coated from the uncoated side. Pressure applied to the upper (uncoated) side transfers the recording fluid to an activated silica-coated receiving sheet to give an intense green print.

Another embodiment of this invention is prepared by melting together 35 parts of refined ouricury wax, 15 parts of refined carnauba wax, 10 parts of high-melting parafiin wax, and 40 parts of petroleum lubricating oil of a Saybolt viscosity and adding to this an amount of 2,2',2" trinitro 4,4',4" tris (dimethylarnino) triphenyl-carbinol equal to 3% of the lubricating oil used. T he mixture was stirred until a clear solutionwas obtained, and the molten wax was then applied to paper by standard coating procedures. A weight of 6 lb./ream is satisfactory, although more, or less maybe added depending upon thecoating properties desired. Pressure transfer of the wax to a heated receiving sheet coated with'attapulgite gives an immediate intense violet (almost blueblack) print. I

The above examples areprimarily useful for one-time copy applications. For a multiple copy transfer sheet one must use a much higher concentration of the nonstaining color base or its dye salt.

Another embodiment of this invention 'for use as a spirit duplicating master sheet is prepared by the use of a transfer sheet which has a coating thereon containing 50% of the nonstaining color base instead of 1.2%. This coating is prepared by melting together 20'parts by weight of refined carnauba wax, 30 parts by weight of chlorinated diphenyl of 48% chlorine content (Arachlor 1248) andmilling this with 50 parts by weight of 2,2'-dinitro-4,4',4"-tris (dimethylamino)-triphenylcarbin0l. The hot melt coating may be used as such or a volatile solvent may be incorporated to give a more fluid system. This coating composition is then applied by standard methods to a base web; and the resultant coated transfer sheet may be used to give a spirit duplicating master sheet. Copies may then be taken from this master sheet by means 'of an alcohol fluid or an ethylene trichloride fluid onto a claycoated receiving sheet.

It should be clearly understood that the invention is not limited to the examples set forth, but is generally applicable to any type of transfer sheet which can utilize for its recording medium a nonstaining color base or a colored dye salt thereof. The commercial advantages of this transfer sheet are many; it functions in the same fashion as ordinary methyl violet oleate transfer paper, yet it will not stain skin or clothing permanently, and toe print is not discharged upon addition of water.

The drawing is a cross-sectional view illustrative of a typical base web (A) coated with a composition containing nonstaining triarylmethane compound (B).

The nonstaining color bases which are used in the practice of the present invention are more particularly described in my co-pending application Serial No. 677,837, filed August 13, 1957.

Having described my invention, I- claim:

1. A nonstaining transfer sheet having upon its surface a coating containing a substantially nonstaining'triarylmethane color base containing at least two dialkylaminosubstituted aryl groups having as a substituent a nitro group and characterized, by a logarithmic dissociat on constant between 2 and 5 which upon transfer to a receiving sheet of high acid strength is converted to the intensely colored salt.

2. The transfer sheet of claim 1 wherein the coating comprises a hard waxy material and a nonvolatile plasticizing fluid of low polarity.

3. The transfer sheet of claim 1 wherein the coating comprises a nonvolatile hydrophobic fluid dispersed in the form of discrete droplets in a hydrophilic colloid binder.

4. The transfer sheet of claim 1 wherein the nonstaining triarylmethane color base is a member of the group consisting of Dinitro Crystal Violet Carbinol Base, its homologs, and their carbinol ethers.

5. The transfer sheet of claim 1 wherein the nonstaining triarylmethane color base is a member of the group consisting of Trinitro Crystal Violet Carbinol Base, its homologs, and their carbinol ethers.

6. The transfer sheet of claim 1 wherein the nonstaining triarylmethane color base is a member of the group consisting of Dinitro Malachite Green Base, its homologs, and their carbinol ethers.

7. A nonstaining transfer sheet having upon its surface a coating containing a substantially nonstaining triarylmethane color base containing at least two dialkylaminosubstituted aryl groups having as a substituent ortho to the central carbon atom a nitro group and characterized by a logarithmic dissociation constant less than 7 which upon transfer to a receiving sheet of high acid strength is converted to the intensely colored salt.

8. A nonstaining transfer sheet having upon its surface a coating containing the intensely colored salt of a substantially nonstaining triarylmethane color base containing at least two dialkylamino-substituted aryl groups having as a substituent a nitro group and characterized by a logarithmic dissociation constant between 2 and 5, said colored dye salt having too low an ionization constant to undergo a permanent chemical reaction with skin.

9. A nonstaining transfer sheet having upon its surface a coating containing the intensely colored salt of a substantially nonstaining triarylmethane color base containing at least two dialkylamino-substituted aryl groups having as a substituent ortho to the central carbon atom a nitro group, said colored salt having too low an ionization constant to undergo a permanent chemical reaction with 10. A manifolding sheet comprising a web having a coating on one side thereof, said coating comprising a solvent and a substantially nonstaining triarylmethane color base containing at least two dialkylamino-substituted aryl groups having as a substituent at nitro group and characterized by a logarithmic dissociation constant between 2 and 5, said nonstaining triarylmethane color base being adapted to produce an intensely colored dye salt upon contact with a surface characterized by high acid strength.

1]. A manifolding sheet comprising a Web having a coating on one side thereof, said coating comprising a solvent and a substantially nonstaining triarylmethane color base containing at least two dialkylamino-substituted aryl groups having as a substituent ortho to the central carbon atom a nitro group, said nonstaining triarylmethane color base being adapted to produce an intensely colored dye upon contact with a surface characterized by high acid strength.

12. A manifolding sheet comprising a web having a coating on one side thereof, said coating comprising a solvent and the intensely colored salt of a substantially nonstaining triarylmethane color base containing at least two dialkylamino-substitutcd aryl groups having as a substituent a nitro group and characterized by a logarithmic dissociation constant between 2 and 5 dispersed in said solvent, said colored salt having too low an ionization constant to undergo a permanent chemical reaction with skin. 7

13. A manifolding sheet comprising a web having a coating on one side thereof, said coating comprising a solvent and the intensely colored salt of a substantially nonstaining triarylmethane color base containing at least two dialkylamino-substituted aryl groups having as a substituent ortho to the central carbon atom a nitro group dispersed in said solvent, said colored salt having too low an ionization constant to undergo a permanent chem ical reaction with human skin.

References Cited in the file of this patent UNITED STATES PATENTS 2,755,201 Webber July 17, 1956 2,755,202 Baion July 17, 1956 2,755,203 Stallmann July 17,1956 

1. A NONSTAINING TRANSFER SHEET HAVING UPON ITS SURFACE A COATING CONTAINING A SUBSTANTIALLY NONSTAINING TRIARYLMETHANE COLOR BASE CONTAINING AT LEAST TWO DIALKYLAMINOSUBSTITUTED ARYL GROUPS HAVING AS A SUBSTITUENT A NITRO GROUP AND CHARACTERIZED BY A LOGARITHMIC DISSOCIATION 